In such an apparatus, the screen wiper includes a wiping strip of flexible elastomeric material which it holds against the swept surface, and which it drives in alternating rotational wiping movement in the well known way.
Motor vehicle glass surfaces, and more particularly windshields, are generally curved, so that it is necessary for the screen wiper to include a screen wiper blade having an articulated structure adapted to force the wiping strip to be in contact over its whole length with the swept surface. The articulated structure also enables the contact pressure of the wiping strip against the swept surface to be substantially homogeneous over the whole length of the wiping strip. For this purpose the articulated structure is arranged to be deformable in a plane which is substantially at right angles to the swept surface, and it holds the wiping strip in this plane of deformation by means of claws.
However, as the screen wiper blade travels over the swept surface in its alternating rotational wiping movement, the plane of deformation of its articulated structure does not remain rigorously perpendicular to the plane of the swept surface, because of the curvature of the latter. As a result, the wiping strip is in contact with the swept surface at an angle which varies according to the position of the screen wiper on the glass.
It has become apparent that this inclination of the wiping strip has a very detrimental effect on the quality of wiping given by the screen wiper blade. A particularly unfavourable situation is the case where, with reference to a motor vehicle windshield, the screen wiper is so designed as to wipe over an end portion at the side of the windshield, which is curved backwards so that it terminates substantially parallel to the lateral riser of the vehicle bodywork that supports the side edge of the screen. The angle of inclination of the wiper strip with respect to the glass is then very large, and tends to adversely effect the efficiency of the screen wiper in that zone.